Three-dimensional Geologic Mapping of Lake County, Illinois: No Small Task

A three-dimensional geologic model for Lake County, Illinois has been made by the Illinois State Geological Survey (ISGS) based on analysis of data from more than 200 exploration boreholes, 24,000 water-well and engineering borehole records, and several miles of geophysical transect data. A data-sharing agreement with the county has facilitated the exchange of digital data, including access to county-wide, high-accuracy datasets that facilitate mapping and quality control of public domain information, such as water-well records. In Lake County, the variability of the continuity and physical characteristics of deposits, typically associated with a number of inset proglacial depositional sequences, necessitates application of both lithostratigraphy and allostratigraphy to map and model geologic surfaces. A number of map units are defined based on genesis, as a practical matter, where bounding surfaces are more readily identified than the boundaries of discrete lithologic units. Throughout the mapping process, ISGS staff have interacted with local decision makers for them to gain an understanding of local natural resource issues, and to provide geologic information to those making decisions. Interactions have included presentations to the county board, local municipalities, industry, and the general public. Future challenges include the design and presentation of the three-dimensional model for the end users.